Drugs, which show cholesterol-lowering effects through the mechanism of inhibiting the activity of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMG-CoA reductase), are generally called “statin”. Among them, examples of the earliest first-generation compounds developed include simvastatin, lovastatin, and pravastatin which are fermentation products, and examples of second-generation compounds include atorvastatin, fluvastatin, rosuvastatin, and pitavastatin which are synthetic drugs.
Among these, rosuvastatin calcium has a structural formula given below and is marketed under the trademark CRESTOR™.

European Patent Application Publication No. EP 0521471 discloses (E)-7-[4-(4-fluorophenyl)-6-isopropyl-2-[methyl(methylsulfonyl)amino]pyrimidin-5-yl](3R,5S)-3,5-dihydroxyhept-6-enoic acid (rosuvastatin) and its sodium salt and hemicalcium salt, and a process for their preparation. According to this patent document, rosuvastatin and its pharmaceutically acceptable salts are obtained by condensation of methyl (3R)-3-[(tert-butyldimethylsilyl)oxy]-5-oxo-6-triphenylphosphoranylidene hexanoate with 4-(4-fluorophenyl)-6-isopropyl-2-(N-methyl-N-methanesulfonyl amino)-5-pyrimidinecarboxaldehyde, followed by deprotection of the 3-hydroxy group, asymmetric reduction of the 5-oxo group and hydrolysis.
Further, WO 00/49014 also discloses a process for the preparation of rosuvastatin and its pharmaceutically acceptable salts, as shown in Reaction Scheme 1 given below. The compound and its pharmaceutically acceptable salts are obtained in WO 00/49104 by reaction of N-(5-((diphenylphosphoryl)methyl)-4-(4-fluorophenyl)-6-isopropylpyrimidin-2-yl)-N-methylmethanesulfonamide (hereinafter, referred to as “DPPO”) with tert-butyl 2-[(4R,6S)-6-formyl-2,2-dimethyl-1,3-dioxan-4-yl]acetate (hereinafter, referred to as “BFA”) in the presence of a base, thus preparing BEM, followed by removal of protecting groups.

Further, WO 04/52867 discloses a process for the preparation of rosuvastatin and its pharmaceutically acceptable salts, which includes the condensation of 1-cyano-(2S)-2-[(tert-butyldimethylsilyl)oxy]-4-oxo-5-triphenylphosphoranylidene pentane with 4-(4-fluorophenyl)-6-isopropyl-2-(N-methyl-N-methanesulfonyl amino)-5-pyrimidinecarboxaldehyde, followed by deprotection, asymmetric reduction of the 4-oxo group and hydrolysis.
WO 07/007119 discloses a process for the preparation of rosuvastatin based on an asymmetric aldol reaction using a chiral titanium catalyst.
Further, WO 07/125547, as shown in Reaction Scheme 2 given below, discloses a method for preparing rosuvastatin or a pharmaceutically acceptable salt thereof, which includes reacting N-(4-(4-fluorophenyl)-6-isopropyl-5-((1-methyl-1H-benzo[d]imidazol-2-ylsulfonyl)methyl)pyrimidin-2-yl)-N-methylmethanesulfonamide (12) with t-butyl 2-((4R,6S)-6-formyl-2,2-dimethyl-1,3-dioxan-4-yl)acetate (BFA) to prepare BEM, and then removing the protecting groups.

However, since currently known methods for the preparation of rosuvastatin hemicalcium salts exhibit low yield and low purity, there is a continuing need for development of alternative processes for the manufacture of pharmaceutically acceptable salts of rosuvastatin.